Secured integrated circuits store confidential data which must remain inaccessible to the end user. Such confidential data may comprise encryption keys, or more generally data protection keys, and data or executable code enabling such keys to be generated or memory-accessed.
Despite all the protections provided in secured integrated circuits, it is still possible to extract the executable code stored by the integrated circuit, by taking advantage of uncontrolled weaknesses thereof. The executable code thus extracted can then be analyzed and/or executed by a compatible but non-protected processor. By having the extracted executable code executed by the unprotected compatible processor, it is possible to access all the data transiting between the processing unit and the memory, including the protection keys.
Certain secured integrated circuits such as those incorporated into smart cards, have a coprocessor to perform “sensitive” calculations, particularly cryptographic calculations handling secret keys. The result is that the coprocessor of such an integrated circuit is mainly targeted by the attacks aiming to discover the secret data handled. Certain attacks, particularly those causing errors in the operation of the coprocessor, are particularly efficient.
Furthermore, the introduction of such a coprocessor into an integrated circuit is not very desirable as it contributes to increasing the complexity of the integrated circuit and therefore the cost thereof.